1. Field of the Invention
This invention relates to a drive unit which is provided in an apparatus for moving up and down a vehicular window pane. More particularly, this invention relates to a technique for preventing an elastic body from protruding from a bracket in an apparatus for moving up and down a vehicular window pane by transmitting the driving force of a drive motor to a shaft member via the elastic body fitted to the bracket.
2. Description of the Related Art
A drive unit for moving up and down a window pane is provided in an apparatus for moving up and down a vehicular window pane. Some drive units have a drive motor and a drive drum on which a wire is wound. Such a drive unit is adapted to move a window pane by rotating the drive drum by means of the driving force of the drive motor in order to move the wire in a predetermined direction, and in turn moving a slider to which the window pane is fitted, as the wire moves.
In the drive unit of the sort mentioned above, the driving force of the drive motor is transmitted to the drive drum via a worm wheel engaging with a worm fixed to a motor shaft, and a shaft member to be rotated integrally with the worm wheel.
FIG. 7 shows a part of the aforementioned conventional drive unit.
The drive unit comprises a worm wheel (a) engaging with a worm fixed to a motor shaft, a bracket (b) to which the worm wheel (a) is fitted, an elastic body (c) provided between the worm wheel (a) and the bracket (b), and a shaft member (not shown) fitted to the bracket (b).
The worm wheel (a) is made of plastics by monolithic molding, for example, and has an annular main wall (d), an external wall (e) projecting from the outer peripheral edge of the main wall (d), and an internal wall (f) projecting from the inner peripheral edge of the main wall (d), the space surrounded by the main wall (d), the external wall (e) and the internal wall (f) being formed as a configuration space. A gear portion is also formed on the external surface of the external wall (e) of the worm wheel (a). Further, projecting portions (g), separated from each other in the peripheral direction are formed so as to project from the internal surface of the main wall (d) into the configuration space.
The bracket (b) is a metallic plate that is pressed into shape and has bent portions. More specifically, the bracket (b) has a substantially disk-like fitting portion (h) and projected supporting leaves (i), separately formed in the peripheral direction of the peripheral edge portion of the fitting portion (h), that are integrally formed. In this case, these projected supporting leaves (i), function to transmit the rotational force of the worm wheel (a), rotated by the drive motor, to the drive drum via the shaft member.
Each of the projected supporting leaves (i), is formed by making an L-shaped slit in the peripheral edge portion of the fitting portion (h) and then bending perpendicularly the portion surrounded by the slit. The formation of the projected supporting leaves (i), through the bending process is followed by the formation of cutout portions (j), in the peripheral edge portion of the fitting portion (h), the cutout portions (j), being open in the radial direction. Further, a slit-like engaging hole (k) is formed in the central portion of the fitting portion (h).
The elastic body (c) is made of rubber material, for example, and includes three main parts (l), extending in the peripheral direction and positioned separately, and narrow coupling portions (m), each for coupling the main parts (l), these being integrally formed. Further, supporting grooves (n), opened outwardly are formed in the central portions of the respective main parts (l).
The supporting grooves (n), of the elastic body (c) are respectively supported by the projected supporting leaves (i), of the bracket (b), whereby each of the main parts (l), of the elastic body (c) are disposed between the projected supporting leaves (i). In this state, the worm wheel (a) is mounted on the bracket (b) from the opposite side of the bracket (b) with the elastic body (c) held therebetween, so that each of the projected portions (g), of the worm wheel (a) may be positioned between the main parts (l) of the elastic body (c). Further, one end portion of the shaft member is made with the engaging hole (k) of the bracket (b) so as to pass the shaft member through the central hole (o) of the worm wheel (a). Then a wire is wound on the side of the other end portion of the shaft member to fit the drive drum (not shown) thereto.
Thus, the worm wheel (a) engages with the worm, which is fixed to the motor shaft which in turn is rotated when the drive motor is rotated, and the drive drum is also rotated as the worm wheel (a) rotates.
When the worm wheel (a) is rotated, the main parts (l), of the elastic body (c) are pressed by the projected portions (g), of the worm wheel (a) to make the elastic body (c) rotate. Simultaneously, the projected supporting leaves (i), of the bracket (b) are pressed against the respective main parts of the elastic body (c), so that the bracket (b) is rotated. Then the shaft member mated with the engaging hole (k) is rotated as the bracket (b) rotates, whereby the drive drum fitted to the shaft member is also rotated.
Thus, the drive drum is rotated when the driving force of the drive motor is transmitted to the worm wheel (a), the elastic body (c), the bracket (h) and the shaft member in this order. The wire wound on the drive drum is moved in the predetermined direction and the window pane is moved up and down as the slider moves.
Incidentally, transmitting the rotational force of the drive motor to the drive drum by placing thc elastic body (c) between the worm wheel (a) and the bracket (b) is aimed to prevent the worm wheel (a) and the bracket (b) from being scraped away or worn down in order to increase a noise-suppressing effect during the rotational operation by avoiding direct contact therebetween.
As stated above, the projected supporting leaves (i), of the bracket (b) are pressed against the main parts (l), of the elastic body (c) and the bracket (b) is rotated when the drive motor is rotated.
However, since the cutout portions (j), are formed in the peripheral edge portion of the fitting portion (h) of the bracket (b) by forming the projected supporting leaves (i), through the bending process, as shown in FIG. 8; there is the possibility that the main parts (l), may be bent and protrude from the cutout portions (j), when the projected supporting leaves (i), of the bracket (b) are pressed by the main parts (l), of the elastic body (c).
If the main parts (l), of the elastic body (c) thus protrude from the cutout portions (j), there occurs a non-conformity, in that the driving force of the drive motor is not properly transmitted to the drive drum.